The present invention relates to a semiconductor device and a method of fabricating the same and, more particularly, to a semiconductor device and a method of fabricating the same preferable when a dielectric interlayer is formed on a gate electrode or when an insulating film is buried in a trench in STI (Shallow Trench Isolation).
After a gate electrode is formed, a silicon oxide (SiO2) film is formed as a dielectric interlayer, or a silicon oxide film is buried in a trench in STI formation.
When a silicon oxide film is formed at a film formation temperature of 500° C. or less in an O3/TEOS ambient atmosphere, a film having flowability, i.e., self-flatness is obtained without any reflow step, so excellent filling characteristics can be obtained.
Unfortunately, a film formation reaction in this case is sometimes very sensitive to and dependent on the surface of an underlayer. Especially when a silicon oxide film is formed on the surface of a silicon nitride (SiN) film, abnormal growth often occurs to form a porous film. This phenomenon is generally called underlayer dependence.
FIG. 11 shows the state of a section when a silicon oxide film is formed in the presence of this underlayer dependence.
An electrode material is deposited on the surface of a semiconductor substrate 10 and patterned to form a gate electrode 11. A silicon nitride film 12 is so formed as to cover the gate electrode 11 and the semiconductor substrate 10. After that, a silicon oxide film 13 as a dielectric interlayer is so formed as to cover the silicon nitride film 12, at a film formation temperature of 500° C. or less in an O3/TEOS ambient atmosphere. Since this silicon oxide film 13 has underlayer dependence, the flowability unique to the O3/TEOS process is lost, and the filling characteristics extremely deteriorate. Consequently, voids 14 are formed in the silicon oxide film 13.
When film formation is performed in an ambient atmosphere at a low O3 concentration, no underlayer dependence is produced. Conventionally, therefore, a method which forms films in two stages is often used. In this method, film formation is performed using low-concentration O3 gas in the initial stage, and then film formation is performed using high-concentration O3 gas.
When films are formed by this method, however, a silicon oxide film as the first layer must have a film thickness of 100 nm or more in order to reduce the underlayer dependence.
Additionally, this silicon oxide film as the first layer formed at a low O3 concentration has poor filling characteristics. In recent microfabricated patterns, trenches are filled with the silicon oxide film as the first layer. This makes the two-stage film formation method difficult to use.
The underlayer dependence can also be eliminated by improving the surface of a silicon nitride film by plasma irradiation. In this case, however, the cost increases because an apparatus for plasma irradiation is additionally required. In addition, the transistor characteristics may deteriorate by plasma damage. Therefore, this method is also difficult to use.
As described above, when a silicon oxide film is formed to fill a portion between gate electrodes or to fill STI in conventional devices, the filling characteristics deteriorate by the underlayer dependence.